The invention pertains to the field of image compression for compact, electronic storage, and, more particularly, to the field of mapping an input document into zones of text and zones of graphics and compressing each zone at a different resolution in terms of bits or pixels per linear inch.
With the growing volume of documents stored in the files of businesses all over the world, and the rising cost of storing such paper documents, there has arisen a need for storing such documents more compactly. Optical disk technology has provided a medium which can store vast quantities of data for archival purposes. However, even with optical disk technology for storage of data, there still exists a need for efficiency in the digitizing of input documents to avoid excess storage of data where extreme resolution is not necessary to accurately reproduce the appearance of the document in a particular zone.
It has been found that most documents have large quantities of blank space at locations between lines of text, between words, in the margins, and in the areas of the document devoted to text data as opposed to graphic data. It has also been found that areas of text in a page may be accurately reproduced with a storage resolution of 100 dots or pixels per linear inch, while graphic data may be accurately reproduced at a storage density of 200 dots per linear inch.
Thus, there has arisen a need for a system which can map an input document into zones of text and zones of graphic data, and which can compress a bit mapped electronic representation of the document such that zones of text are stored at 100 pixels per linear inch while graphic zones are stored at 200 pixels per linear inch.